It is known to provide garage door openers or operators with upper and lower position limits, and with sensitivity or torque limits. Generally manual adjustment or selection is provided to allow the user or the installer of the door operator to set position limits which coincide with the fully open and fully closed positions of the door, and to set sensitivity limits which permit sufficient torque to move the door throughout its complete range in both opening and closing direction, but not enough torque to damage the door. A given model of operator may be intended for use on light doors, which might be damaged by too much torque, as well as heavy doors. It is important to match the operator to the door by the sensitivity setting to achieve proper operation and no damage due to the door.
The sensitivity setting and the position limits are also used in obstruction detection for stopping the door to prevent damage to the obstruction. By using the maximum sensitivity which is consistent with proper door operation the damage to an obstruction can be minimized. It is a requirement that an obstruction detection feature be utilized during door movement except in the last inch prior to the closed position. Thus the closed position limit is useful in identifying the door position above which obstruction detection is armed.
It is also known, as disclosed in U.S. Pat. No. 4,638,433 to Schindler, to use a microprocessor control for a garage door operator and to use that control to establish limits by a learning method. That is, by manipulating switch inputs to the controller, the installer or user can place the control in a program mode and run through a door operation procedure which causes the controller to determine the position limits and up and down force limits. The position limits are constant values throughout operation of the opener. If any changes of position limits are required, they are accomplished by repeating the program or learn mode. The force limits have an offset in addition to the learned force which is large enough to accommodate changes in force due to temperature or other variations. Each of the up and down force limits is a single value which is applied over the travel range of the door, irrespective of local force requirement at particular door positions.
The practice of setting force limits with offsets large enough to anticipate changing conditions results in low sensitivity to the detection of obstructions. It is preferred that such an offset be small to attain high sensitivity. Thus another method of accommodating changes in door opening and closing force is desired. The effective floor position may change as a result of heaving due to frost or by a build-up of ice on the floor, for example. It is thus desirable to automatically change the closed limit position to reflect the actual end of door travel, and to accomplish such a change in limit without manually entering the program mode.
It is also desirable to provide a high sensitivity range at the lower portion of door closing travel. This lower range of travel is the most likely place to encounter obstructions, especially small children and toys, and a higher sensitivity in that region will minimize the risk of harmful impact.